Backport r45540 to introduce OpenSSL::OPENSSL_LIBRARY_VERSION

Let's backport r45540.
It introduces OpenSSL::OPENSSL_LIBRARY_VERSION. It's a new feature and marked as [EXPERIMENTAL]. So usually it shouldn't be backported to stable branches.
But it's convenient to check linked OpenSSL runtime version, and valuable to confirm openssl security fixes are applied.
A changeset is quite simple.